Accumulating epidemiologic and experimental evidence indicates that certain nutritionally essential trace elements, including zinc, may play an important role in cholesterol metabolism and ultimately in atherosclerotic process. The underlying mechanics of their action on cholesterol metabolism have, however, been meagerly documented. This study is designed to investigate (a) the intestinal absorptive processes of dietary cholesterol, (b) the chemical and physical characteristics of chylomicrons formed during active intestinal transport of cholesterol, and (c) the metabolic turnover of chylomicron cholesterol as affected by the nutritional status of zinc. This work will be conducted using growing and mature rates fed semi-purified diets. The diets will be formulated to produce a marginal deficiency of zinc in order to avoid a drastic reduction in diet consumption and early mortality as seen in an acute severe deficiency of the element, and to simulate a suboptimal level of zinc intake which may exist in human population. The specific methods for the determination of intestinal absorption of dietary cholesterol involve the use of the in situ ligated intestinal loop technique and the cannulation of the intestinal lymphatic duct. The procedure consists of the administration of 14C-labeled cholesterol into a specific anatomical segment of the small intestine and the measurement of either the disappearance out of the intestine or the appearance into the lymphatic system of the label administered. Chylomicrons formed during active transport of cholesterol will be obtained by the method of lymphatic duct cannulation. Studies on subsequent isolation and characterization of the lipoprotein will include the use of ultracentrifugal, chromatographic, electron microscopic, and gel electrophoretic techniques. The measurement of plasma clearance of the chylomicrons labeled with 14C C-cholesterol and the transfer of chylomicron apoproteins labeled with 3H-leucine to high-density lipoproteins will be performed after intravenous administration of the labeled chylomicrons. These studies will involve the withdrawal of known volumes of blood via the orbital sinus at specific time intervals and determination of the radioactivity in the plasma and in apoproteins separated by SDS gel electrophoresis.